Boom Supersonic has sketched out broad details of a unique propulsion system it envisions as powering a supersonic passenger jet coming after its now-in-development airliner Overture.
Blake Scholl, the Colorado start-up’s founder and chief executive, applied in October 2023 for a patent covering a conceptual propulsion architecture involving traditional low-bypass turbojets supplemented by a separate system composed of multiple deployable fans.
At high speed, the turbojets would provide thrust and the fans would be stowed within the aircraft’s structure, out of the airstream. But at slow speed the fans would extend out, providing thrust during take-off and landing.
That combination could give a supersonic aircraft optimal fuel efficiency in the supersonic realm but enable it to operate quietly – in compliance with aircraft noise regulations – near the ground, says the patent application, published in April by the United States Patent and Trademark Office.
Scholl confirms to FlightGlobal that Boom sees promise in the design, saying it could solve limitations imposed by traditional turbines. He notes that designers of supersonic jets today face a choice between using higher-bypass turbofans, which are quieter but less efficient at supersonic speed, or lower-bypass turbines, which are more efficient but too loud near the ground.
He says the concept does not apply to Overture – which he refers to as “Overture one” – but rather to a future and faster follow-on.
“What you’re seeing in that patent is just some of the thinking that we’ve already started around… How is there a successor to Overture that can fly faster and be quieter?” he says. “This is really next-generation technology, and we put a marker out there with the patent.”
Boom already has its hands full developing Overture – an envisioned 64-80 passenger jet capable of flying at Mach 1.7, with an end-decade service-entry goal. The complexities and expense of the project are enormous, and large existing engine makers have declined to participate, saying they instead are focused on developing more-efficient engines for next-generation subsonic aircraft. Therefore, working with Florida Turbine Technologies, Boom is leading in-house development of a medium-bypass turbofan for Overture called Symphony. Scholl says that project is progressing well.
“The thing we’ve realised on Overture one is that the single-biggest challenge [for]… first-generation supersonics is managing the trade-off between cruise efficiency and being quiet for take-off and landing,” Scholl adds. “You have to make the fan bigger to be quiet, and you have to make the fan smaller to be efficient” at cruise.
That trade-off, he adds, is one reason Boom settled on designing Overture to fly at M1.7. The company had previously aimed to have it fly at M2.2.
The patent application includes sketches of an aircraft with four traditional turbojets hung under gull-shaped wings, and with groups of fans stowed behind panels or doors, “within an aerodynamic profile of the aircraft”. One possible configuration has eight fans stowed in the aircraft’s tail. Another has fans stowed within its wings. At slow speed, the fans would deploy – similar to landing gear – and provide thrust, “thus mimicking a higher-bypass-ratio engine during lower-speed operation”, the application says. The turbojets could power the fans, either mechanically or electrically.
